1. Field of the Invention
The present invention relates to a receptacle type optical transmitter and/or receiver module.
2. Description of the Related Art
In an optical communication system using an optical fiber as a transmission line, a laser diode module (LD module) is used to introduce light emitted from a light emitting component (e.g., laser diode) into the optical fiber. In the LD module, the light emitting component and the incident end face of the optical fiber are fixed in a given positional relationship, and a condenser lens is interposed between the light emitting component and the incident end face of the optical fiber. Further, a photodiode module (PD module) is used to couple signal light emerged from an optical fiber to a photodetecting component (e.g., photodiode). In the PD module, the emergent end face of the optical fiber and the photodetecting component are fixed in a given positional relationship, and a condenser lens is interposed between the emergent end face of the optical fiber and the photodetecting component.
The primary type of such an LD module and a PD module as key devices in optical communication was a pigtail type such that an optical component and an optical fiber are integrated. However, a receptacle type optical module allowing separation of the optical component and the optical fiber is now desired because a mounting space for an optical module is reduced with a reduction in device size and an extra fiber length is accordingly difficult to settle. In mounting an optical module such as an LD module on a printed wiring board by soldering like a surface mount type component or a through hole mount type component, a so-called pigtail type optical module with an optical fiber cord is not suitable as the optical module.
That is, the optical fiber cord usually has a nylon coating, and the nylon coating has a low resistance to heat at about 80° C., so that it is melted in the soldering step. Furthermore, the optical fiber cord itself invites inconveniences in accommodation and handling at a manufacturing location, causing a remarkable reduction in mounting efficiency to the printed wiring board. Accordingly, to allow a soldering process for the optical module and reduce a manufacturing cost, the provision of a so-called receptacle type optical module is indispensable. There has been developed a receptacle type optical transmitter or receiver module for transmitting or receiving an optical signal wherein an optical component and electric circuit components are sealed together with resin by utilizing the merits of the receptacle type as mentioned above.
A conventional receptacle type optical transmitter module is composed of a receptacle type LD module, a printed wiring board on which a driver LSI for driving the LD module is mounted, and a lead frame functioning as an interface between the printed wiring board and a mother board. The LD module and the printed wiring board having the driver LSI are electrically connected by connecting lead terminals of the LD module and conductor patterns formed on the printed wiring board through conductive adhesive or wire bonding, for example. The assembly of the LD module and the printed wiring board is then sealed with a mold resin to thereby configure the optical transmitter module.
A process of assembling an opto-electrical integrated module for transmitting an optical signal is generally composed of the following three steps. (1) The first step is lead forming of an LD module. (2) The second step is fixedly mounting the LD module with the formed leads on a printed wiring board. (3) The final step is sealing the LD module and the printed wiring board with resin, thus completing the opto-electrical integrated module. The purpose of lead forming of the LD module is to make the leads of a general CAN type coaxial device match with the pattern pitch of the printed wiring board and to relax the application of stress to a bonding portion and root portion of each lead in bonding the LD module to the printed wiring board.
The conventional receptacle type optical transmitter or receiver module has the following problems.
(1) It is essential that an optical transmitter or receiver module can be mounted on a mother board by reflow soldering, so as to utilize the merit of its small size. However, a general LD module does not have heat resistance (240° C.) in reflow soldering, so that the LD module is mounted on the printed wiring board after reflow soldering. Further, another LD module having heat resistance is special in structure and therefore expensive.
(2) In connecting the optical module such as an LD module to the printed wiring board, lead forming of the optical module is required in order to make the leads match with the pattern pitch of the printed wiring board and to relax the stress applied to the bonding portion and root portion (glass sealed portion) of each lead. As a result, the connection distance between the optical module and the printed wiring board becomes long, causing a difficulty of high-speed operation.
(3) In the case that only the optical module malfunctions, it is impossible to replace or repair only the optical module in the condition that the electric circuit assembly having no problems is left. Further, also in the case that only the electric circuit assembly malfunctions, a similar problem arises.